The present invention relates to a pressure reducer for hydraulic brake systems comprising a piston penetrating a sealing ring with play, a piston head of enlarged diameter forming a valve together with the sealing ring, which valve is able to separate an inlet chamber and an outlet chamber in the housing, and, in the rest position, a first spring presses the piston against a stop in the outlet chamber and a second spring presses the sealing ring in the same direction against a step of the housing to thereby define the valve stroke.
In a known pressure reducer of this type, such as disclosed in FIG. 4 of German Patent DE-AS No. 1,555,387, the piston may be loaded by a spring whose initial tension determines the change-over pressure of the pressure reducer. With a sealing ring inserted, a second spring concentrically enclosing the piston exerts pressure on the sealing ring, thus reliably pressing it against the step. The valve stroke so established will bring about an exactly defined change-over point as the inlet pressure increases. However, the second spring will have a retarding effect on the quick opening of the valve upon a drop in the inlet pressure, since the axial displacement of the sealing ring required to this end will be possible only if the inlet port side pressure has decreased to the point that the initial tension of the second spring has been overcome. By means of a sealing washer, the other end of this second spring presses a second annular seal against the front surface of the inlet chamber, the second annular seal serving as a piston seal. The thus produced deformation of the sealing ring material will lead to a wear which cannot be neglected.
It is also known from FIGS. 1 and 3 of German Patent DE-AS 1,555,387 to dispense with such a second spring for the loading of the valve sealing ring to ensure a quick opening of the valve upon a drop in the inlet pressure. Then, however, the sealing ring will not reliably abut against the housing step in the rest position. Because of the thus undefined valve stroke the change-over pressure is not exactly determined.